In electronic systems that utilize processing units, for example a base station of a telecommunication network, overheating can occur in central processing units (CPUs), or digital signal processing units (DSPs), or other processing circuits.
FIG. 1 is an example of a typical base station node, comprising a main processing unit 101 and a plurality of peripheral processing units 103 to 121 (for example DSPs) arranged in a hierarchical tree topology. Processing units 103, 109 and 117 are connected to the main processing unit 101 via branches BR11, BR12 and BR13, respectively. The processing units 103, 109 and 117 and the branches BR11 to BR13 can be considered as a first hierarchical level. The remaining processing units and respective branches are connected in a second hierarchical level.
If any of the processing units shown in FIG. 1 become overloaded, cooling systems are commonly used to reduce the occurrence of hotspots.
There are several known ways to cool a CPU, DSP or hotspot. The simplest is to supply a fixed amount of air (air flow) over the CPU, DSP or hotspot, such that heat energy is convectively transported away from the CPU, DSP or hotspot.
More complex systems use sensors for measuring the temperature of one or several CPUs, DSPs or hotspots, such that the amount of cooling can be controlled accordingly. For example, if a high temperature is detected, the cooling operation can be increased (for example by increasing the flow of air and/or supplying cooler air). Likewise, if a lower temperature is detected, then less cooling can be provided (for example by decreasing the flow or air, i.e. airspeed, and/or air temperature).
In the simplest solution, the cooling system is oversized (has excess cooling capacity), leading to inefficient cooling. Another disadvantage of such oversized cooling systems is the high level of noise associated with large cooling systems.
In more complex situations such as radio base stations, other problems may arise. For example, in the case where no more airflow is available (for example because cooling fans are running at maximum capacity), there is no way of decreasing the temperature, other than shutting down the entire radio base station. This type of emergency shutdown may be catastrophic with respect to a communication system, especially if multiple radio base stations shut down on a single hot day. Alternatively, some form of energy consuming device (such as an air conditioner) can be used to lower the temperature of the incoming air.
To prevent catastrophic shut downs, conventional cooling systems are designed with large engineering safety margins in order to handle very high ambient temperatures that might be very rare (such as the hottest day in August). Such conventional systems have the disadvantage of having to be oversized for a particular application.